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Ozawa, Kazumi; Tanigawa, Hiroyasu; Morisada, Yoshiaki*; Fujii, Hidetoshi*
Fusion Engineering and Design, 98-99, p.2054 - 2057, 2015/10
Times Cited Count：1 Percentile：8.33(Nuclear Science & Technology)Reduced activation ferritic/martensitic steel, as typified by F82H, is a promising candidate for structural material of DEMO fusion reactors. To prevent plasma sputtering, tungsten (W) coating was essentially required. This study aims to examine the irradiation effects on hardness and microstructure of vacuum-plasma-spray coated W-F82H steel, with a special emphasis on the impacts of grain-refining induced by frictional stir processing (FSP). It was revealed that the hardness of the VPS-FSP W after ion-irradiation to 5.4 dpa at 800
C were not remarkably changed, where bulk W usually exhibited significant irradiation hardening.
Tanigawa, Hiroyasu; Ozawa, Kazumi; Morisada, Yoshiaki*; Noh, S.*; Fujii, Hidetoshi*
Fusion Engineering and Design, 98-99, p.2080 - 2084, 2015/10
Times Cited Count：15 Percentile：72.09(Nuclear Science & Technology)The vacuum plasma spray (VPS) technique has been investigated as the most practical method to form Tungsten (W) layer as a plasma facing material in fusion devices. The issues are the thermal conductivity and the strength of VPS-W, i.e., the thermal conductivity of VPS-W were significantly lower than that of the bulk W, and the hardness of VPS-W is much less than that of the bulk W. These are mainly caused by the porous structure of VPS-W. In order to solve these issues, friction stir processing (FPS) was applied on VPS-W in this study. It was suggested that FSP can contribute to significant improvement both in mechanical and thermal properties of VPS-W coating.
Nozawa, Takashi; Ozawa, Kazumi; Asakura, Yuki*; Koyama, Akira*; Tanigawa, Hiroyasu
Journal of Nuclear Materials, 455(1-3), p.549 - 553, 2014/12
Times Cited Count：19 Percentile：76.99(Materials Science, Multidisciplinary)SiC/SiC composite is a promising candidate material of fusion DEMO reactor. This paper aims to identify its damage tolerance and strength anisotropy by various characterization techniques such as acoustic emission (AE) monitoring, electrical resistivity (ER) measurement, and digital image correlation (DIC). The AE results identified that damage accumulation initiated prior to the proportional limit stress (PLS) by both tensile and compressive loadings for 2D composites. The preliminary AE waveform analysis implied that this AE detect strength corresponds to initiation of micro-cracking but the stress-strain curve shows further linearity due to the strong interfacial friction. Then fiber sliding occurred near the PLS, followed by the non-linearlity of the curve. The preliminary tensile test results using a notched specimen also suggest notch insensitivity of the composites in any loading directions. The detailed failure mechanism will eventually be discussed with ER and DIC results.
Nozawa, Takashi; Kim, S.*; Ozawa, Kazumi; Tanigawa, Hiroyasu
Fusion Engineering and Design, 89(7-8), p.1723 - 1727, 2014/10
Times Cited Count：13 Percentile：64.60(Nuclear Science & Technology)A SiC/SiC composite is a promising candidate material for the advanced fusion DEMO blanket. For the design of the DEMO, the stability of high-temperature strength of SiC/SiC composites needs to be identified. Additionally, strength anisotropy needs to be clarified because of its unique fabric architecture. This study therefore aims to evaluate mechanical properties by various modes at elevated temperatures, eventually providing a stress envelope for the design. A P/W Tyranno-SA3 fiber reinforced CVI SiC matrix composite with multilayered SiC/PyC interface was evaluated in this study. Tensile and compressive tests were conducted by the SSTT specifically arranged for the high-temperature use. In-plane shear properties were contrarily estimated by the off-axial tensile method assuming that the mixed mode failure criterion is valid for composites. All tests were performed in vacuum. The preliminary test results indicate no degradation of both proportional limit stress (PLS) and the ultimate tensile strength at temperatures below 1000C. Similarly, no significant degradation of high-temperature compressive and in-plane shear properties were identified, finally providing the stress envelope at elevated temperatures for the design.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
Fusion Engineering and Design, 88(9-10), p.2543 - 2546, 2013/10
Times Cited Count：16 Percentile：72.00(Nuclear Science & Technology)A SiC/SiC composite is a promising candidate for a fusion DEMO blanket. Due to the inherent quasi-ductile failure of composites, determining failure scenario for this class of composites is undoubtedly important to develop design codes in practical use of them. This study aims to evaluate the failure behavior of the quasi-ductile SiC/SiC composites to provide a strength map. For this purpose, detailed tensile, compressive and in-plane shear failure behaviors were evaluated by the acoustic emission (AE) technique. The AE results distinguished damage accumulation processes by wavelet analysis. Of particular emphasis is that matrix cracking occurred prior to the PLS by both tensile and compressive loadings because the rough-surface of SiC fibers resulted in the strong frictional stress at the fiber/matrix (F/M) interface. In this paper, an updated failure envelope will be provided by referring the actual matrix cracking stresses as more realistic and reasonable failure criteria.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
Ceramic Materials for Energy Applications II, p.95 - 110, 2012/11
This study aims to identify failure behavior of SiC/SiC composites by varied test modes. For this purpose, acoustic emission (AE) was applied to detect composites' failure. Tensile and compressive tests were conducted for a plain-weave (P/W) chemical vapor infiltration (CVI) composite. Various loading angles were applied to discuss an anisotropic issue. AE results distinguished damage accumulation processes in axial and off-axial loading cases. Specifically, test results indicated a clear difference of damage density between tensile and compressive tests. This study also classified the characteristic failure modes by separately discussing localized variations of power within a time series by wavelet analysis.
Nozawa, Takashi; Ozawa, Kazumi; Choi, Y.-B.*; Koyama, Akira*; Tanigawa, Hiroyasu
Fusion Engineering and Design, 87(5-6), p.803 - 807, 2012/08
Times Cited Count：37 Percentile：90.67(Nuclear Science & Technology)A SiC/SiC composite is a candidate material for a demonstration fusion power reactor. Considering the inherent anisotropy of composites with variety of fabric architecture is required to precisely predict axial and off-axial mechanical properties by various failure modes. This study evaluated crack propagation behavior by the various modes to provide a strength anisotropy map and we discussed a methodology to analytically predict this trend. The strength anisotropy maps identified for various fabric orientations clearly indicate that the composites failed by the mixed modes. Specifically, due to the axial anisotropy, five individual modes such as tensile/compressive strengths in the axial/transverse directions, respectively, as well as the in-plane shear strength, are identified to be essential. In this study, with the analytical criterion based on the Tsai-Wu model, the strength anisotropy could satisfactorily be described.
Matsui, Yoshinori; Takahashi, Hiroyuki; Yamamoto, Masaya; Nakata, Masahito; Yoshitake, Tsunemitsu; Abe, Kazuyuki; Yoshikawa, Katsunori; Iwamatsu, Shigemi; Ishikawa, Kazuyoshi; Kikuchi, Taiji; et al.
JAEA-Technology 2009-072, 144 Pages, 2010/03
JAEA-Technology-2009-072.pdf:45.01MB
"R&D Project on Irradiation Damage Management Technology for Structural Materials of Long-life Nuclear Plant" was carried out from FY2006 in a fund of a trust enterprise of the Ministry of Education, Culture, Sports, Science and Technology. The coupled irradiations or single irradiation by JOYO fast reactor and JRR-3 thermal reactor were performed for about two years. The irradiation specimens are very important materials to establish of "Evaluation of Irradiation Damage Indicator" in this research. For the acquisition of the examination specimens irradiated by the JOYO and JRR-3, we summarized about the overall plan, the work process and the results for the study to utilize these reactors and some facilities of hot laboratory (WASTEF, JMTR-HL, MMF and FMF) of the Oarai Research-and-Development Center and the Nuclear Science Research Institute in the Japan Atomic Energy Agency.
Usami, Koji; Ichise, Kenichi; Numata, Masami; Endo, Shinya; Onozawa, Atsushi; Takahashi, Hiroyuki; Kikuchi, Taiji; Ishikawa, Kazuyoshi; Yoshikawa, Katsunori; Nakata, Masahito; et al.
no journal, ,
In the R&D Project on Irradiation Damage Management Technology for Structural Materials of Long-life Nuclear Plant, the specimens to be obtained by coupling irradiation between JOYO and JRR-3 is necessary to establish the evaluation method by using the irradiation damage indicator of them. Therefore, the techniques for assembling of JRR-3 re-irradiation capsule in the Waste Safety Testing Facility (WASTEF) were developed to perform the coupling irradiation. The techniques contributed to the first coupling irradiation in the world.
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu
no journal, ,
Interfacial properties of unidirectional CVI SiC/SiC minicomposites reinforced with Hi-Nicalon Type-S (HNLS) and Tyranno-SA3 were evaluated. Only HNLS minicomposites with 240- and 1150-nm-thick PyC interphases exhibited a pseudo-ductile behavior. Brittle fracture behavior of other minicomposites was attributed primarily to quite low fiber volume fraction. The HNLS minicomposites with 240-nm-thick exhibited an ultimate tensile strength equivalent to 79-104% of the fiber bundle strength but only 70-85% of the strength of 1150-nm-thick. Based on hysteresis loop analysis, sliding stress estimated for the 240-nm-thick appeared to be about 1.4 times as that for the 1150-nm-thick. This shows that both composites satisfy the GLS condition, but the composite with the thicker interphase could not achieve its fiber bundle strength, probably due to the lower interfacial sliding stress.
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu
no journal, ,
Tensile and interfacial properties of unidirectional SiC/SiC model composites reinforced with Hi-Nicalon Type-S fibers with innermost pyrolytic carbon (PyC) layer thickness of 
240 and 1150 nm (TypeS-240 and TypeS-1150, respectively) were evaluated by unloading/reloading cyclic tensile tests and single fiber push-out tests. Effective fiber bundle strength in the TypeS-240 and -1150 composites were 79-104% and 70-85%, compared with the original fiber bundle strength. According to the analytic results using hysteresis loops of tensile curves, interfacial sliding stress of the TypeS-1150 estimated to be about 0.7 times as large as the TypeS-240. This tendency was also confirmed by the single fiber push-out tests. These composites showed quasi-ductility, but it is considered that the composite with the thicker interphase could not achieve its fiber bundle strength, probably due to the lower interfacial sliding stress.
Ozawa, Kazumi; Koyanagi, Takaaki*; Taguchi, Tomitsugu; Nozawa, Takashi; Tanigawa, Hiroyasu; Kondo, Sosuke*; Hinoki, Tatsuya*
no journal, ,
A SiC/SiC composite is a promising candidate functional/structural material for fusion DEMO reactor. To examine the effects of transmuted H mainly on microstructural cavity formation, the monolithic NITE-SiC with 6wt% Y
O
-AlO sintering additive system were ion-irradiated to 10 dpa at 1000C nominally with 130 appmHe/dpa, and 40 or 400 appmH/dpa, respectively. In SiC grains, tiny cavities with 2 nm formed densely. However, it is revealed that H could not remarkably impact on cavity formation (size, density) in the condition studied. The influence of cavities formed along SiC-YAG grain boundary (GB) on cavity swelling seems to be also small, possibly attributed to its quite low density, even though the cavity size formed is three to five times larger than the size in CVI-SiC matrix in the same irradiation condition. Additional investigation of the microstructural evolution in YAG grain and SiC-YAG GB is a future plan.
Ozawa, Kazumi; Koyanagi, Takaaki*; Taguchi, Tomitsugu; Nozawa, Takashi; Tanigawa, Hiroyasu; Kondo, Sosuke*; Hinoki, Tatsuya*
no journal, ,
no abstracts in English
Ozawa, Kazumi; Nozawa, Takashi; Toyoshima, Kazuoki*; Tanigawa, Hiroyasu; Hinoki, Tatsuya*
no journal, ,
no abstracts in English
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu
no journal, ,
no abstracts in English
Nozawa, Takashi; Tanigawa, Hisashi; Hirose, Takanori; Ozawa, Kazumi; Tanigawa, Hiroyasu; Enoeda, Mikio
no journal, ,
A hot isostatic press (HIP) process is a key technology to fabricate a first wall (FW) with cooling channels of the fusion blanket system, and development of the destructive/non-destructive inspection techniques is strongly required. Conventional Charpy impact test is a well-established test method but this technique cannot be applied to the thin-walled cooling channels of the actual component. In contrast, the authors recently proposed a brand new method utilizing a miniature torsion specimen. This study first applied this developmental technique with a miniature specimen to evaluate the HIP joint of the model blanket structure and to evaluate its mechanical properties. The test results show minor difference of the fracture energy but clearly identified that the yield and maximum strength of the HIP joint were equivalent to those of the base metal, eventually identifying the sound structural stability of the HIP joint of the model blanket structure.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
A SiC/SiC composite is a candidate material for nuclear fission and fusion applications. Generally, composites failure initiate from inherent internal/surface flaws and hence these flaws as potential failure origins need to be adequately considered in qualification of the material for the practical application. Focusing on the surface flaw issue, identifying notch sensitivity is essential to judge cracking tolerance of composite materials. To date, many extensive work evaluated notch sensitivity of various types of composites and it has almost been concluded that SiC/SiC composites with moderate fiber/matrix interface are notch insensitive by fast fracture monotonically loading mechanical tests. This study aims to further evaluate the notch effects by various failure modes such as cyclic tensile loading/unloading. For that purpose, various damage monitoring methods such as acoustic emission, digital image correlation, etc. are supplementarily adopted.
Nozawa, Takashi; Park, J.-S.*; Nakazato, Naofumi*; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
Silicon carbide is a candidate nuclear materials because of low-activation and superior irradiation resistance as well as perceived various characteristics inherently featured as prominent engineering ceramics and a continuous fiber reinforced composite has generally been developed due to brittleness of SiC itself. Of many material parameters for design, validation of high temperature durability at approximately 1000C is essential. Understanding of anisotropy of woven composite strength is also very important. Besides, developing comprehensive model to predict composite strength by various modes with a limited data set. This study aims to summarize the features of fracture behavior by tensile, compressive and shear at elevated temperatures. With consideration of the prediction model, we finally obtain the high temperature strength anisotropy map.
Ozawa, Kazumi; Koyanagi, Takaaki*; Nozawa, Takashi; Kato, Yutai*; Kondo, Sosuke*; Tanigawa, Hiroyasu; Snead, L. L.*
no journal, ,
A silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite is a promising candidate material for an advanced fusion DEMO blanket. High-dose irradiation experiments were performed with our special focuses on understanding; (1) integrity of the Hi-Nicalon Type-S (HNLS) composites, (2) functionality of thin pyrocarbon (PyC) /SiC multilayer, and (3) clarifying the mechanism underlying degradation, as feedback to R&D on SiC/SiC composites. The materials used in this study were plain-weave HNLS composites produced via the chemical vapor infiltration process. Neutron irradiation was conducted in the HFIR at ORNL. The peak neutron fluence was ~1.0
10
n/m
(E 
0.1 MeV, equivalent to ~100 dpa) at nominal irradiation temperatures of 300, 500, and 800C. Results of post irradiation experiments including 1/4-four-point flexural tests, SEM, and TEM observation were reported.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
A SiC/SiC composite is a promising candidate material for various engineering applications. For the practical design of composite components, the detailed failure mechanism need to be clarified since composites exhibit unique quasi-ductility in fracture. Focusing on the surface flaw issue, identifying notch sensitivity is essential to judge damage tolerance of composite materials. To date, it is convinced that composites with moderate fiber/matrix interface are generally notch insensitive. However, recent work by the authors claimed indicative notch sensitivity of advanced SiC/SiC composites by the off-axial tensile loading case. This study aims to identify the detailed damage accumulation behavior of this class of composites to fully understand their notch sensitivity. For that purpose, the digital image correlation (DIC) technique, which becomes a potential powerful tool to understand the detailed failure mechanism of composites, is specifically adopted to get a local strain distribution profile near the notch tip.
